Laboratory and pilot-scale development of the ambient temperature ferrite process

Expanded Title:

This project was commissioned in response to an opportunity to implement the ambient temperature ferrite process (ATFP) as part of the CSIR ABC Desalination Process that was to be installed at the ERPM site in Germiston, Gauteng, treating 100 ML/d of acid mine drainage (AMD). The lab results indicated a relationship between the operating pH, retention time, ferrite seed concentration and feed ferrous iron concentration in removing the ferrous iron from solution and forming ferrite intermediate on the ferrite seed present. The contact stabilisation reactor was fed Harmony Gold AMD, which contained Fe(II) concentrations 280-890 mgFe/L. The contact stabilisation reactor was capable of removing all of the aqueous ferrous iron from the AMD if the system was operated at a pH of at least 9. For the systems, the feed ferrous iron was removed from as high as 890mgFe/L with seed concentrations of 3gFe/L and retention times as low as 10 minutes, although 15 minutes was required for a system operating with a pH of 9. For solids removal, a clarifier operating with an up flow velocity of 5m/h was required, resulting in 14 times thickening of the ferrite solids (seed plus intermediate). However, when the ATFP pilot plant was operated under these conditions, the system failed within a few days, indicated by a build-up of brown-coloured material in the process. Numerous changes to the operating procedure were made, but it was shown that it was difficult to maintain high seed concentrations in the system using the existing infrastructure, since the freshly produced ferrite seed had different settling properties to the mine ferrite. This led to a steady deterioration in the solids quality and ultimately process failure. Therefore, it was not possible to operate a successful ATFP treating AMD using lime. The process should first be proven at laboratory scale using AMD and lime before another pilot plant is built and operated.